Critically Evaluated Rate Coefficients for Free‐Radical Polymerization, 5^,

Abstract

Propagation rate coefficients, k p , for free-radical polymerization of butyl acrylate (BA) previously reported by several groups are critically evaluated. All data were determined by the combination of pulsed-laser polymerization (PLP) and subsequent polymer analysis by size exclusion (SEC) chromatography. The PLP-SEC technique has been recommended as the method of choice for the determination of k p by the IUPAC Working Party on Modeling of Polymerization Kinetics and Processes. Application of the technique to acrylates has proven to be very difficult and, along with other experimental evidence, has led to the conclusion that acrylate chain-growth kinetics are complicated by intramolecular transfer (backbiting) events to form a mid-chain radical structure of lower reactivity. These mechanisms have a significant effect on acrylate polymerization rate even at low temperatures, and have limited the PLP-SEC determination of k p of chain-end radicals to low temperatures (<20 8C) using high pulse repetition rates. Nonetheless, the values for BA from six different laboratories, determined at ambient pressure in the temperature range of À65 to 20 8C mostly for bulk monomer with few data in solution, fulfill consistency criteria and show excellent agreement, and are therefore combined together into a benchmark data set. The data are fitted well by an Arrhenius relation resulting in a preexponential factor of 2.21 Â 10 7 L Á mol À1 Á s À1 and an activation energy of 17.9 kJ Á mol À1 . It must be emphasized that these PLP-determined k p values are for monomer addition to a chain-end radical and that, even at low temperatures, it is necessary to consider the presence of two radical structures that have very different reactivity. Studies for other alkyl acrylates do not provide sufficient results to construct benchmark data sets, but indicate that the family behavior previously documented for alkyl methacrylates also holds true within the alkyl acrylate family of monomers.Arrhenius plot of propagation rate coefficients, k p , for BA as measured by PLP-SEC.

Photocrosslinkable Star Polymers via RAFT-Copolymerizations with N-Ethylacrylate-3,4-dimethylmaleimide

“…It thus appears that termination is rather high in this system, which, however, is in conflict with findings by Gilbert et al, who qualitatively found that termination in aqueous NIPAm polymerization is low [35]. As propagation in acrylate and NIPAm polymerization is similar [36,37]-note that a slow propagation may also lead to high amounts of terminated chains after the same extent of monomer conversion-lower amounts of terminated RAFT polymer would thus be anticipated according to Gilbert's findings, which clearly is not the case. It is therefore more likely that some other mechanism than biradical termination leads to deactivation of chains under loss of the RAFT-units.…”

On the Use of Quantum Chemistry for the Determination of Propagation, Copolymerization, and Secondary Reaction Kinetics in Free Radical Polymerization

“…Since its invention in the late 1980s, PLP-based techniques have substantially improved the quality of the experimental measurements of rate parameters in FRP, particularly for propagation reactions. These techniques have also been widely used for the study of the homopolymerization and copolymerization of various monomers [5][6][7][8][9][10][11][12][13][14][15][16][17][18].…”

Modeling of Polymerization Kinetics and Processes—from Voting to Toting

“…Unauthenticated Download Date | 5/12/18 9:15 AM formally, intramolecular chain transfer to polymeracts to interrupt chain growth, thus compromising the simple correlation between polymer size and pulse time [8], as d escribed above. There have been other complicating scientific issues-cottage ind ustries always mushroom around a big, successful venture-but these have been the main ones.…”